A vacuum-pressure adjuster connected to a vacuum pump or a vacuum line connected to a vacuum pump for maintaining a constant vacuum pressure in the vacuum line is disclosed, for instance, in Public disclosure of Japanese patent application filed by the applicant of the present application and provisionally published as No. 59-175832.
In FIG. 3, there is shown such a vacuum-pressure adjuster that a diaphragm 83 provided with a valve 82 for adjusting the flow amount of air into a vacuum system 81 is so provided in a section as to partition it into a first chamber 84 at the side of the valve 82 and a second chamber 85 opposite to the valve 82, and in this case, the first chamber 84 is in communication with atmospheric air through an opening 95 and the second chamber 85 is in communication with atmospheric air through a pilot valve 86 and opening 94 and moreover, the second chamber 85 is in communication with the vacuum system 81 through a small opening 91 of the required size.
In the drawing, numeral 87 designates a diaphragm, 94a an air-filter, 86a an air-flow inlet, 88 a spring adapted to push the diaphragm 87 downwardly and 89 a pressure-adjusting screw for the spring.
The vacuum-pressure adjuster 40 causes vacuum pressure of the vacuum system 81 to act on the fourth chamber 92 and the second chamber 85 in such a manner that the pilot valve 86 may automatically adjust the open degree of the air-flow inlet 86a due to the balance between the vacuum pressure of the fourth chamber 92 and the pressing force of the spring 88. Due to the difference between the amount of inflow of air from the air-flow inlet 86a and the amount of air flowing out from the opening 91, the degree of vacuum of the second chamber 85 can be adjusted, as the result of which pressure changes in the vacuum system 81 become pressure changes in the second chamber 85 until they are transferred to the diaphragm 83 and then the valve 82 is displaced either upwardly or downwardly, thus adjusting the amount of air flow into the vacuum system 81 and maintaining the pressure in the vacuum system 81 at a constant level.
Although this kind of vacuum-pressure adjuster acts to maintain a constant level of vacuum pressure of the whole vacuum system throughout, to which it is connected, yet, its use has heretofore been infeasible for such a purpose that it is connected to some high-vacuum system so as to maintain the pressure in it at a constant high-vacuum level, and at the same time, it is required to provide another vacuum system, as divergent from the high-vacuum system, kept at a vacuum level lower than that of the high-vacuum system.